Fentanyl, a selective μ-opioid agonist, is an analgesic or anesthetic adjunct. Lately, the palliative treatment of cancer pains has particularly progressed, and fentanyl has been establishing a secure status as an opioid drug alternative to morphine. Further, when QOL (quality of life) of a patient with cancer pains is considered, transdermal administration is one of the most convenient routes.
One of the preferred embodiments of the transdermal administration is to use a patch preparation wherein a drug layer (containing a drug and a pressure-sensitive adhesive), formed on a backing layer, is covered with a release liner. In general, when a drug is transdermally administered using a patch preparation, it is desirable that a drug be dissolved in an adhesive in view of its diffusion and skin permeation. Further, to secure a predetermined amount of a drug to be absorbed, it is desirable to mix a transdermal absorption enhancer in a pressure-sensitive adhesive.
Thus, it is common for a pressure-sensitive adhesive to contain liquid ingredients such as solubilizers, solubilizing adjuvants, transdermal absorption enhancers, and the like. However, containing such ingredients posed a problem in that the cohesive force of an adhesive base was reduced. When the cohesive force of an adhesive base is reduced, the skin permeability of a drug tends to be also reduced. For this reason, if liquid ingredients in a pressure-sensitive adhesive are increased for the purpose of enhancing the diffusion and skin permeation of a drug, it may, on the contrary, deteriorate the skin permeability of the drug.
Generally, basic drugs such as fentanyl have low skin permeability. Due to this property, when fentanyl is contained in a pressure-sensitive adhesive, it is imperative to add a large amount of liquid ingredients in the pressure-sensitive adhesive to attain adequate drug diffusion and skin permeation. However, since a large amount of liquid ingredients added causes reduced cohesive force of an adhesive base due to the reason described above, it raised a problem that sufficient skin permeability of a drug could not be achieved.
To solve the above problem, fentanyl-containing patch preparations are disclosed in Patent Documents 1 to 4. More specifically, known patch preparations include; patch preparations in reservoir formulation and multilaminate formulation (Patent Document 1), a patch preparation containing an organic acid salt, a styrene-isoprene-styrene block copolymer and polyisobutylene (Patent Document 2), a patch preparation containing N-methyl-2-pyrrolidone (Patent Document 3), and a patch preparation in which fentanyl particles are suspended in more than 1 solvated silicone-based pressure-sensitive adhesive (Patent Document 4).    Patent Document 1: Japanese Patent Laid-Open No. 61-37725    Patent Document 2: Japanese Patent Laid-Open No. 10-45570    Patent Document 3: Japanese patent Laid-Open No. 2000-44476    Patent Document 4: Japanese Patent Application (International application) Laid-Open No. 2006-513160